A semiconductor memory device is provided. A semiconductor memory device is a memory device embodied by using a semiconductor such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phosphide Inp, etc. Typically, a semiconductor memory device may be either a volatile memory device or a non-volatile memory device.
A volatile memory device is a memory device where stored data becomes lost if power is not supplied. Examples of volatile memory devices include a static RAM (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM) and so on. A non-volatile memory device is a memory device where stored data remains even when power is not supplied. Examples of non-volatile memory devices include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable and programmable ROM (EEPROM), flash memory, phase-change RAM (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM), ferroelectric RAM (FRAM), etc. Flash memory, which may be the most common and well-known non-volatile memory device, includes a NOR-type memory device and a NAND-type memory device.
Semiconductor memory devices typically includes memory cells that each store at least one data bit. Semiconductor memory devices may include single level cells or mufti-level cells. A single level cell stores one data bit, and mufti level cells store two or more data bits.
Semiconductor memory devices typically also include one or more peripheral circuits for driving the memory cells. However, as the number of data bits stored in each memory cell increases, the design of the one or more peripheral circuits becomes more complex. For example, the design of the peripheral circuit when three data bits are stored in one memory cell is more complex than that of the peripheral circuit when two data bits are stored in one memory cell, and area of the peripheral circuit when three data bits are stored in one memory cell is higher than that of the peripheral circuit when two data bits are stored in one memory cell.